Fiber optics have had a large impact on transmission techniques, due in part to the large bandwidth and high data rate capability of fiber optics. Wavelength division multiplexed (WDM) networks employ a transmission technique that allows multiple wavelengths (i.e., channels) to be transmitted on a single fiber and further increases the bandwidth of an optical network.
It is highly desirable to maintain constant optical power in all channels in order to minimize inter-channel crosstalk. Crosstalk occurs in an optical transmission system when separate WDM channels interfere with one another due to inadequate channel protection or unequal power levels between adjacent channels. Crosstalk results in undesirable noise in a given channel as a result of optical signal leaking from other channels. As the number of channels carrying signals for WDM transmissions increases, the impact of crosstalk between adjacent channels and other WDM channels also increases. Crosstalk should be minimized to receive a better signal-to-noise ratio on the receiving end of an optical transmission on a WDM channel. O'Mahony et al., in an article entitled “The Design of a European Optical Network,” discloses design issues for a large-scale WDM network traversing Europe and identifies crosstalk as a design issue that must be considered.
Power spectrum monitoring and management is critical for amplified, add-drop, WDM networks, because power fluctations caused by added or dropped channels can create crosstalk. Conventional power monitoring techniques employ spectrometers or wavelength division demultiplexors for monitoring the power of channels in a WDM network. These techniques are complex, costly to implement, not readily scalable and do not include techniques for mitigating crosstalk. Consequently, a need exists for providing a low-cost, scalable power monitoring system that can be used to mitigate crosstalk.